Lebanon Crop Management Video

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19 July 2016

Staging Soybeans –R stage Critical Considerations

Del Voight Penn State Extension
Many fields of soybeans are actively growing and there some general information one needs to become familiar with what the plant is going through at this time.  Many fields at this time are in the R2 growth stage.  What does this mean? R2 is identified by first inspecting for the presence of  the flowers. Once flowers are observed within the top 2 nodes of the top  of the plant(full flower) the plant is in the R 2 stage.   Plants have two main stages V and R. The V stands for vegetative that is to say the stage that the plant germinates emerges and puts leaves on the main stem. Then the R stage which refers to the reproductive stage.  This stage marks a change in the plant from  simply growing green leaves to begin to prepare the metabolism and prepare to produce an ear or a pod.  In many cases both stages exist with Soybeans they will continue to put new leaves on while flowering.  Typically they will stay in the V stages for about 40 days or more.  Once in the R stage the plant will stay in R stages until harvest time.
Most fields should be in the R2 stage.  Now you know what I am referring to pertaining to stages.  At this stage the flowers are self pollinating.  The pods are being formed within the flower.   Intercanopy humidity and temperature will now factor into whether the pod forms and aborts.    The plants 300 bu/acre potential is now being dictated by temperature, pest pressure,  stress from drought or water.  Typically 60-75% of the total flowers fail to produce a pod.  The plant will stay in the flowering condition for a 30 day period but will move from R2-R3 in about 2 weeks. R3 is marked by the formation of a pod that is 3/16th of an inch at any of the top 4 nodes. The top third of the soybean leaves directly impact yield.  Therefore scouting is required to ensure limited damage from insect or disease.
Penn State Extension and Soybean Board funding of field research has been working on determining benefits of fungicides applied at  R3 to date the data suggest that  applications of fungicides average a return to the application of about 3-4 bu/acre.  Consider applications If there is visible disease and the weather in the two week forecast is wet and high humidity benefits might be greater than  if conditions remain dry and low humidity.Also realize that wheel traffick will reduce yields based on boom width.  Wider booms have less impact. For instance Ohio State Extension engineers have shown about a 2.5 bu/acre loss with a typical 45 foot boom and a 1.5 bu/acre loss with a 90 foot boom. Wheel width also may reduce the impact of trafficking in the soybeans.  Consider custom applications if wider boom width is not available on your farm.  Check for the presence of soybean aphids, stink bugs, bean leaf beetles and grasshoppers to ensure that they will not reduce soybean canopy by R3 to ensure yield is protected through the pod filling stages.  Check the Agronomy Guide for Pesticide options, rates and application specifications.

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